1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification, a semiconductor device generally refers to a device which can function by utilizing semiconductor characteristics; an electro-optical device, a semiconductor circuit, and an electronic device are all included in the category of the semiconductor device.
2. Description of the Related Art
A technique by which transistors (also referred to as thin film transistors (TFTs)) are formed using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). As materials of semiconductor thin films applicable to the transistors, silicon-based semiconductor materials have been widely used, but oxide semiconductors have been attracting attention as alternative materials.
For example, disclosure is made of a transistor whose active layer is formed using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) (see Patent Document 1).